What causes arthritis

Arthritis develops when the protective cartilage in your joints wears down or your immune system attacks the joint lining. The reason depends on which type you have. Osteoarthritis happens from years of use—the cartilage that cushions bone ends simply breaks down over time, like a tire wearing thin. Rheumatoid arthritis is different: your immune system mistakenly treats joint tissue as a threat and inflames it. Other types have their own causes, from infections to metabolic problems to injuries that heal incorrectly.

The process is not sudden for most people. Osteoarthritis typically takes years or decades to develop. Rheumatoid arthritis can start more quickly, sometimes over weeks or months. Either way, once cartilage damage or immune inflammation begins, it tends to get worse without treatment because the joint cannot repair itself the way other tissues do.

Key Takeaways

  • Osteoarthritis results from cartilage breakdown due to age, weight, repetitive stress, or previous injury to the joint.
  • Rheumatoid arthritis occurs when your immune system attacks the lining of joints, and it often runs in families or is triggered by infection.
  • Other arthritis types stem from gout (uric acid crystals), infections, or autoimmune conditions unrelated to rheumatoid arthritis.
  • Risk factors include age over 50, female sex, family history, obesity, and jobs or sports involving repetitive joint stress.
  • Understanding your type of arthritis matters because treatment approaches differ significantly between wear-and-tear and immune-driven forms.

Osteoarthritis: wear and tear on joints

Osteoarthritis is the most common type and develops when cartilage gradually thins. Cartilage is the smooth, rubbery material covering the ends of bones inside a joint. When it wears away, bone rubs against bone, causing pain, stiffness, and swelling. This happens because cartilage does not have its own blood supply—once it is damaged, your body cannot easily repair it.

Several things speed up cartilage breakdown. Age is the biggest factor; most people over 65 show some cartilage loss. Excess weight puts extra pressure on joints, especially knees, hips, and ankles. Repetitive motion—from a job, sport, or hobby—can wear cartilage faster. A previous injury to a joint, even one that healed years ago, increases the risk that osteoarthritis will develop there later. Women are more likely to develop osteoarthritis than men, particularly after age 50.

Osteoarthritis usually starts in one or two joints and may spread to others over time. It is not contagious and does not involve the immune system attacking the joint, which is why it is treated differently from rheumatoid arthritis.

Rheumatoid arthritis: an immune system error

Rheumatoid arthritis happens when your immune system mistakenly attacks the synovium, the thin membrane lining your joints. This triggers inflammation that causes pain, swelling, and warmth in the affected joints. Over time, the inflammation can damage the cartilage and bone underneath. Unlike osteoarthritis, rheumatoid arthritis often affects multiple joints at once, usually in a symmetrical pattern—both hands, both knees, both feet.

The reason your immune system attacks your own joints is not fully understood, but genetics and environment both play a role. If a parent or sibling has rheumatoid arthritis, your risk is higher. Certain infections may trigger the condition in people who are genetically predisposed. Smoking also increases risk. Women are two to three times more likely to develop rheumatoid arthritis than men, and it often starts between ages 30 and 60.

Rheumatoid arthritis is an autoimmune disease, meaning your body's defense system is misdirected. This is why treatment focuses on calming the immune response, not just managing pain. Early treatment can slow or stop joint damage, which is why seeing a doctor soon after symptoms start matters.

Other types and their causes

Gout develops when uric acid builds up in your blood and forms crystals in joints, usually the big toe. It is triggered by diet (red meat, organ meats, certain seafood, alcohol), dehydration, or kidney problems that prevent uric acid from being cleared. Gout attacks come suddenly and are extremely painful but often resolve within days.

Infectious arthritis occurs when bacteria, viruses, or fungi enter a joint, usually through an injury or bloodstream infection. Lyme disease, caused by a tick bite, can trigger arthritis weeks or months later. Hepatitis C and HIV can also cause joint inflammation. Treating the underlying infection often stops the arthritis.

Psoriatic arthritis develops in some people who have psoriasis, a skin condition. Lupus and other systemic autoimmune diseases can cause arthritis as one of many symptoms. Ankylosing spondylitis primarily affects the spine and is linked to a specific genetic marker. Each type has different causes and requires different approaches to treatment.

Age and genetics as risk factors

Age is one of the strongest predictors of arthritis. Cartilage naturally becomes more brittle and less able to repair itself as you get older. Osteoarthritis is rare before age 40 but becomes common after 60. Rheumatoid arthritis can start at any age but peaks in the 40s and 60s.

Family history matters for both types. If your parents or siblings have osteoarthritis, your risk is higher—though this reflects both shared genes and shared lifestyle factors like activity level and weight. Rheumatoid arthritis has a stronger genetic component; having a first-degree relative with it roughly doubles your risk. Certain genetic markers, like HLA-DR4, are associated with rheumatoid arthritis, but having the gene does not mean you will develop the disease.

Genes load the gun, but environment pulls the trigger. You might inherit a tendency toward arthritis but never develop it if you maintain a healthy weight, stay active, and avoid joint injuries. Conversely, someone without a family history can develop arthritis from years of repetitive stress or obesity.

Lifestyle and injury as contributing factors

How you use your joints over a lifetime shapes your arthritis risk. Jobs involving repetitive motion—assembly line work, construction, nursing—increase osteoarthritis risk in the joints used most. Athletes in high-impact sports like running or football have higher rates of knee and ankle osteoarthritis. Carrying excess weight puts constant strain on weight-bearing joints, particularly knees, hips, and lower back.

Previous injuries are a major factor. A torn meniscus in the knee, a broken bone that healed improperly, or a severe ankle sprain can lead to osteoarthritis in that joint years or decades later, even if the injury seemed to heal completely. The damage to cartilage or the joint's alignment may not cause problems immediately but sets the stage for earlier wear.

Smoking increases the risk of rheumatoid arthritis and may worsen osteoarthritis progression. Heavy alcohol use can trigger gout and may increase rheumatoid arthritis risk. Conversely, regular moderate exercise, maintaining a healthy weight, and protecting joints from injury reduce arthritis risk significantly.

When inflammation becomes chronic

In osteoarthritis, the inflammation is a response to cartilage damage—your body is trying to repair the joint but the process becomes chronic and painful. In rheumatoid arthritis, the inflammation is the primary problem; the immune system keeps attacking even though there is no infection or injury to fight.

Chronic inflammation in any joint leads to progressive damage. Swelling reduces the joint's range of motion. Bone spurs may form as the body tries to stabilize a damaged joint. Muscles around the joint weaken from disuse, which makes the joint less stable and accelerates further damage. This is why early treatment matters—stopping inflammation early can prevent or slow this cascade.

The longer inflammation continues untreated, the more permanent the damage. This is especially true for rheumatoid arthritis, where joint damage can become irreversible within the first year or two if the immune attack is not controlled. Osteoarthritis damage is also permanent, but slowing its progression can preserve function for years.

Frequently Asked Questions

Can arthritis be caused by weather or cold?

Cold and damp weather do not cause arthritis, but many people with existing arthritis report that their symptoms worsen in cold or rainy weather. This may be due to changes in barometric pressure affecting joint fluid or simply that people move less in bad weather. The underlying arthritis was already present.

Does cracking your knuckles cause arthritis?

No. Studies have found no link between knuckle cracking and arthritis development. Cracking is the sound of gas bubbles forming and popping in joint fluid. It may be annoying to others, but it does not damage cartilage or cause arthritis.

Can you get arthritis from an old sports injury?

Yes. A previous injury to a joint—even one that seemed to heal completely—increases the risk of osteoarthritis developing in that joint later. The initial damage to cartilage or changes to the joint's alignment can lead to uneven wear over time. This is why protecting joints from injury matters for long-term joint health.

Is arthritis hereditary?

Genetics play a role in both osteoarthritis and rheumatoid arthritis, but neither is purely hereditary. Rheumatoid arthritis has a stronger genetic component; having a family member with it increases your risk. However, many people with the genetic predisposition never develop arthritis, and many without a family history do develop it.

Can you prevent arthritis if it runs in your family?

You cannot eliminate the risk, but you can reduce it significantly. Maintain a healthy weight, stay physically active, protect your joints from injury, avoid smoking, and limit alcohol. If you have a family history of rheumatoid arthritis, talk to your doctor about early warning signs so treatment can start quickly if symptoms appear.